As the selections are stored in an array you have to go through the array of all points of an object and check if they are selected or not. The can be easily be done with a COFFEE-Expression or a COFFEE Node.
Have a look at the COFFEE SDK and the "GetPointSelection()" and "IsSelected (point_no)" commands.
Kind regards,
Arndt "Vreelonaut" von Koenigsmarck
http://www.vreel-3d.de
http://www.vonkoenigsmarck.de
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